Adipo-mimetic motion-control hydration system pack

ABSTRACT

An improved hydration system for runners that provides superior motion control. Fluid is contained within a flexible bladder and pack, and attached to the waist. The pack is constructed of comfortable, elastic, and thermally insulating fabric. When attached to the waist, tension in the fabric compresses the bladder against the user and dampens motion. Along with reduced thickness of the fluid-filled bladder, uniform distribution of fluid in the bladder contributes to motion control and is provided by placement of the zipper in a horizontal orientation across the lower portion of the pack. Additional stability is achieved by attachment of waist straps at angles above horizontal, thereby increasing tension across the top portion of the pack, preventing it from flopping away from the user&#39;s body.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Provisional Patent ApplicationSer. No. 60/478,419, filed Jun. 16, 2003.

FEDERALLY SPONSORED RESEARCH

Not Applicable

SEQUENCE LISTING OR PROGRAM

Not Applicable

BACKGROUND

1. Field of Invention

This invention relates to the field of personal hydration systems usedby runners or joggers.

2. Discussion of Prior Art

Running, cycling, and other forms of exercise produce an increased needfor water intake to compensate for that lost by respiration,perspiration, and renal output. This need, if not met, may become lifethreatening during prolonged high-intensity activity in hot weather. Itis therefore desirable to be able to carry on one's person an adequatesupply of water or other hydrating fluid.

Although hydration systems are in common use by cyclists, prior arthydration systems for runners have not met one essential designcriterion: The device must utilize a stable, non-irritatingwaist-mounted system with sufficient motion control to minimize bounceand sway. Manufacturers of back-mounted hydration packs have attemptedto adapt these devices for runners so that they may be worn about thewaist. These waist-mounted packs are essentially back-mounted designsretrofitted with a waistband, and are constructed without considerationof the unique needs of runners.

Because a cyclist has little oscillatory body motion compared to arunner, a back-mounted pack can be attached with loose shoulder straps.Furthermore, since there is little motion of the pack relative to theuser's back, the pack can be constructed of inelastic woven nylon orpolyester fabric. However, running produces substantial running-relatedmovement of the muscles about the waist and hip area. To achievesufficient motion control, the waistband must be cinched tight toprevent motion of the pack. However, as the tension of the waistbandincreases, so does the pressure on the user's muscles, tendons, andother tissues. As a result, the user of such packs is faced with adilemma: if too loose, the pack will have too much motion, and if tootight, the result is discomfort and possible injury. Since the tissue ofthe waist area is in motion, the pack itself must be sufficiently pliantso that it can move with the runner. Inelastic fabric does not allow forthis, and may represent a potential source of injury to runners who usesuch systems.

Another problem that arises with the use of inelastic cloth relates tothe ability of the fabric to prevent motion of the bladder within thefabric pack. The basic design of all hydration packs is a bladder withina fabric bag or pack. When the pack is constructed of inelastic fabric,the maximum tension against the bladder is achieved only when thebladder is filled to the point where its volume is equal to the volumeof the fabric compartment. As fluid is drained from the bladder, thevolume of the bladder decreases, but the volume of the fabric bag doesnot. The bladder is thus free to bounce around, producing excessivemotion of the system. Some systems utilize additional straps to take upthe slack created by decreasing bladder volume; however, these must becontinually tightened as the bladder is drained, and this isinconvenient.

Prior art hydration systems suffer from additional problems. Because ofgravity and the flexible nature of the bladder, fluid pools in thebottom of the bladder. This produces an uneven distribution of the fluidwithin the bladder, producing sloshing as a result of the increasedmoment of inertia of the fluid within the bottom portion of the pack.

Given that hydration systems are most useful in hot weather, thermalinsulation is essential to prevent fluid warming. However, prior artpacks employ a design in which additional thermal insulation is sewninto the fabric pack, and this increases both the complexity and cost ofconstruction. Ideally, the fabric used in construction of the pack wouldhave a combination of the desired mechanical and thermal properties soas to provide both motion control and thermal insulation.

OBJECTS AND ADVANTAGES

It can be seen that prior-art hydration systems for runners suffer froma number of problems, including:

-   -   a) insufficient motion control resulting from inefficient        immobilization and attachment of the bladder and pack;    -   b) discomfort due to inelastic fabric;    -   c) inefficient incorporation of thermal insulation leading to        complexity of construction resulting in increased production        costs.

Accordingly, several objects and advantages of the present inventioninclude:

-   -   a) to provide a means for attaching a flexible fluid-filled        bladder to the waist such that motion of the bladder is dampened        and minimized as a result of compression against the runner's        body;    -   b) to prevent pooling of liquid in the lower portion of the        bladder while maintaining ease of cleaning and air drying of the        bladder;    -   c) to provide a means for attaching the flexible fluid-filled        bladder to the waist such that the pack is comfortable and does        not irritate sensitive underlying tissue;    -   d) to provide efficient incorporation of thermal insulation to        the hydration system;

Other objects and advantages will become apparent from a considerationof the following description and drawings.

SUMMARY

The following invention is a personal hydration system designed forrunners and joggers, and consists of a flexible bladder to containpotable fluid. The bladder is enclosed in a flexible, elastic fabricpack and fastened about the waist of the user. The flexible fluid-filledbladder is restrained by compression against the user's body by thetensioned outer fabric layer of the pack. Because tension in the elasticouter fabric layer is maintained automatically as the bladder volumedecreases with fluid consumption, compression of the bladder against theuser's body is maintained at all times, providing constant motioncontrol. In the present design, the zipper, in addition to allowinginsertion of the bladder into the pack, also functions as a structuralelement. By placing the zipper in a horizontal orientation across thelower portion of the pack, the pack is unable to stretch in the regionof zipper attachment. As a result, the zipper acts as a baffle,constricting the lower portion of the bladder and preventing excessivepooling of fluid within this region. This reduces the moment of inertiaof the bladder within the lower portion, resulting in significant motioncontrol. An additional structural feature involves the angle ofattachment of the webbing that wraps around the waist of the user.Placement of the webbing at an angle above horizontal relative to thehorizontal axis of the pack produces increased tension in the upperportion of the pack, preventing this portion of the pack from floppingaway from the user's body, thereby increasing stability of the pack as awhole.

DRAWINGS

Drawing Figures

FIGS. 1A and 1B show front and rear elevation views of the bladder,respectively. FIGS. 1C, 1D, 1E, and 1F show rear elevation views ofbladders with different aspect ratios and different distribution of thewidest extent about the vertical axis.

FIG. 2A is a front elevation view of the pack assembly showing placementof the zipper and angle of the attached webbing. FIG. 2B is afragmentary front elevation view of the pack assembly showing alternatemeans of attachment of waist straps to the pack.

FIG. 3 is a front elevation view of the pack assembly showing placementof upper pack tensioning straps.

FIG. 4 is a fragmentary front perspective view of the pack.

FIGS. 5A and 5B are cross-sectional views taken about line 5 of FIG. 4and show the effect of the elastic pack fabric on compression of theenclosed bladder.

FIGS. 6A and 6B are cross-sectional views taken about line 6 of FIG. 4and show the effect of zipper placement on the vertical distribution offluid in the bladder.

FIGS. 7A and 7B are side perspective views of the pack showing theeffects of both sipper placement and angle of webbing attachment on thedistribution of fluid within the pack.

FIGS. 8A, 8B, and 8C show distribution of forces across the face of thepack and the enclosed bladder as a function of webbing angle and zipperplacement.

REFERENCE NUMERALS IN DRAWINGS

-   11 Bladder cap 34 Right tension strap buckle-   12 Bladder opening 42 Right waist strap-   13 Tube outlet coupling 43 Tri-glide/ladder lock-   20 Hydration pack 44 Right buckle element-   21 Outer fabric layer 45 Left buckle element-   22 Inner fabric layer 46 Left waist strap-   25 Zipper 80 Runner-   26 Bladder compartment stitching 90 Bladder-   31 Left upper tensioning strap 91 Bladder—front face-   32 Right upper tensioning strap 93 Bladder—rear face-   33 Left tension strap buckle

DETAILED DESCRIPTION

FIG. 1A discloses a bladder 90 filled through a cap 11 and whichcontains fluid for drinking. The bladder is constructed of two layers ofdurable food- or beverage-grade plastic film such as PVC or urethane. Afront layer 91 is apposed to a rear layer 93 shown in FIG. 1B and sealedaround the edges using a suitable method such as ultrasonic,dielectric/RF welding, adhesive, or thermal impulse sealer. The twolayers thus define an inner compartment that holds a potable fluid.Fluid exits via a tube outlet coupling 13 that attaches to the frontface and which has a lumen contiguous with the interior of the bladder.A tube (not shown) attaches to the outlet coupling and can be used todeliver fluid to the mouth of the user in a number of possible ways notconsidered here. Prior art hydration systems generally use a bladderwith a rectangular outline and rounded corners. The present design usesa bladder with an outline that has no straight edges or corners.Although there are a number of possible variations, the present designuses a shape that approximates an ovoid. The key defining features ofthe bladder geometry are these: the bladder is defined by vertical andhorizontal axes denoted as V and H respectively, where V is the heightof the bladder at its greatest vertical extent, and H is the width ofthe bladder at its greatest horizontal extent, where 0.5≦(V/H)≦2.0. InFIGS. 1A and 1B, V/H=1.0. FIG. 1C shows a bladder where V/H=2.0, andFIG. 1D shows a bladder where V/H=0.5. In all cases, the bladders shownhere exhibit bilateral symmetry about the vertical axis V, but do notnecessarily show bilateral symmetry about the horizontal axis H.Furthermore, although FIGS. 1A through 1D show that the widest extent Hof the bladder is within the lower region of the bladder, this is notthe only possible configuration; as seen in FIG. 1E, it is possible toconfigure a bladder in which the widest extent H is in the upper regionof the bladder. Also, if the widest extent H is located at the midpointof the vertical axis V, then the bladder may also exhibit bilateralsymmetry about the horizontal axis H (FIG. 1F). Therefore, it can beseen that there is a wide range of possible bladder configurationssubject to the constraint that there are no sharp corners, i.e., thebladder does not have a rectangular, trapezoidal, or other n-sidedgeometric shape, but rather, has rounded edges and approximates anovoid.

FIG. 2A is a more detailed view of the invention. The bladder 90 (hiddenhere) is contained within a pack 20 which is composed of at least twolayers of thermal insulating elastic fabric, with an outer layer 21being shown here attaching to an inner layer 22 which is hidden in thisview. In the preferred embodiment, 3-5 mm thick neoprene fabric is used,and is seamed about the edges. The bladder 90 is removed from andinserted into the pack 20 via a zipper 25. The pack 20 is mounted aboutthe waist by means of a left side waist strap 46 which is attached tothe left side of the pack 20 on one end and attaches on the other end toa left buckle element 45. A right side waist strap 42 is attached to theright side of the pack 20 on one end and attaches on the other end to aright buckle element 44. The left buckle 45 and the right buckle 44 snaptogether to constrain the pack 20 about the waist of a user 80. FIG. 2Bshows an alternate means of attachment of the waist strap 42 to thepack. Rather than sewing the right webbing strap 42 directly to theright side of the pack 20, a fastening element (tri-glide orladder-lock) 43 is attached to the pack, and the waist strap 42 threadsthrough the fastening element 43. This method could also be employed onthe left side as well (not shown). Using this method, thetri-glide/ladder-lock 43 allows adjustability of the waist strap lengthat the point of attachment to the pack 20, allowing for greaterflexibility in waist strap adjustment if desired by the user.

Two key features of the pack design contribute to motion control of theenclosed fluid-filled bladder. Because of the elastic nature of thefabric, the pack is comfortable to wear, as it flexes to move with themovements of the runner. However, the elastic nature of the fabric canallow fluid to pool in the bottom of the bladder as a result of gravity.To counteract this while still maintaining comfort, placement of thezipper in a horizontal orientation across the lower portion of the packrestrains the fluid in this region. The mechanism for this is apparent:given that the zipper is inelastic, it prevents stretching of the packmaterial and distension of the bladder at this region. As a result, aportion of the fluid within the bladder is forced upwards, resulting ina more even vertical distribution of fluid within the bladder. Intesting, it was found that the ideal distance of the zipper from thebottom of the pack, shown by the arrow z, was approximately one fourththe length of the vertical axis, shown here by the arrow V. However,depending on the shape of the bladder, ratios of z/V of between 0.15 and0.5 were found to be suitable.

The fluid-filled bladder behaves very similarly to adipose tissue, andif a sports bra is used as a model for comparison, the design can bethought of as an approximation of the adipose tissue of breasts, whichare restrained in a similar fashion by elastic fabric that produces acompression of the adipose tissue against the user's body. For thisreason, the present design is adipo-mimetic in that the flexiblefluid-filled bladder mimics the behavior of adipose tissue. Althoughmost of the support and immobilization comes from the elastic tensionedfabric of the pack, the zipper, by functioning similarly to an underwire in a sports bra, provides an additional level of support due to itsinelastic properties.

Placement of the waist straps 42 and 46 at angles relative to thehorizontal axis of the pack H produces further stability. In testing itwas found that placement of the straps parallel to the horizontal axisresulted in unequal distribution of tension across the pack, with theresult being that the upper portion of the pack would tend to fall awayfrom the user's back, producing an unpleasant flopping action. Byplacing the straps at an angle θ above the horizontal axis, greatertension is produced across the upper portion of the pack, which is thentensioned firmly against the user's back. Testing of prototypes foundthat an angle θ of between 15° and 60° produced the most efficientmobilization of the pack. An additional element of construction involvesa row of stitching 26 through front and back layers of the pack, thusdefining a compartment within which the bladder is constrained, andpreventing lateral movement of the bladder within the pack. The taperedportions of the pack lateral to the stitching 26 act as transition zonesbetween the large bladder-containing portion of the pack and the morenarrow waist straps 42 and 46. These transition zones act to distributethe tension generated by the waist straps 42 and 46 more uniformlyacross the bladder.

An alternate embodiment to the angled strap arrangement is shown in FIG.3. Rather than placing the waist straps at an angle, the purpose ofwhich is to increase tension across the top portion of the pack, it isalso possible to increase tension through the use of additionaladjustable straps. A left upper tensioning strap 31 attaches to the leftupper portion of the pack 20, and is secured to the left waist webbingstrap 46 by means of a buckle 33. Similarly, a right side uppertensioning strap 32 attaches to the up right portion of the pack and issecured by means of a right buckle 34. It is also possible to omit thebuckles 33 and 34 and simply sew an inelastic cord or strap onto boththe left and right upper lateral portions of the pack. Functionally, theresults of these different embodiments are similar, namely to increasetension across the upper portion of the pack, preventing it fromflopping away from the user's back. However, because of the simplicityof construction, attaching the waist straps to the pack at an angleabove horizontal is the preferred embodiment, as it results insimplified construction and reduced production costs.

FIG. 4 is a fragmentary perspective view of the pack 20. FIGS. 5A and 5Bare cross-sectional views taken about the line 5 shown in FIG. 4. InFIG. 5A, no bladder is inserted, and it can be seen that the outer andinner fabric layers 21 and 22 are in direct apposition. FIG. 5B showsthe pack after insertion of the fluid-filled bladder 90. The bladder isconstrained within the pack by the stitching 26. Because the pack isunder significant tension when placed about the user's waist, andbecause the user's back is relatively non-deformable, the bladderdistorts only the outer layer 21. As a result, regardless of whether thebladder is empty, full, or somewhere in between, there is never any voidspace within the pack to allow the bladder to slosh around. This is inmarked contrast to hydration packs constructed of inelastic nylon orpolyester fabric. These packs have a compartment of constant volume, yetthe enclosed bladder has variable volume that is a function of theamount of fluid contained within. Therefore, even if the bladder isstuffed snugly into one of these packs when it is completely full, afterjust a few sips of fluid, the bladder volume decreases but the packvolume does not, and the result is void space that allows the bladder tobounce around within the pack.

FIGS. 6A and 6B are cross-sectional views taken about the line 6 shownin FIG. 4. FIG. 6A shows the pooling of fluid in the bottom of thebladder 90 when the zipper is placed horizontally either at the very topor very bottom of the pack, or in a vertical orientation. As a result ofgravity and the elastic outer fabric layer 21, the fluid within thebladder pools at the bottom, resulting in an uneven verticaldistribution of fluid. The thickness of the bladder, defined as thegreatest extent normal to the surface of the user's back, is shown bythe arrow D. FIG. 6B shows the effect of zipper placement of the presentinvention. Because the zipper 25 is inelastic, distension of the bladderand the pack at the region of zipper placement is reduced. As a result,the bladder is pinched at this point, and a portion of the fluid isforced into the upper portion of the bladder, producing a more evenvertical distribution of fluid within the bladder 90. Here, thethickness of the bladder, shown by the arrow D, is reduced relative toFIG. 6A. The zipper thus becomes not just a means for accessing theinterior of the pack, it also becomes an important structural elementthat contributes to the motion control of the bladder and pack. Again,using a sports bra as a model for comparison, the inelastic zipper, withrespect to the upper pool of fluid, functions similarly to an underwire,resulting in increased support and motion control. An additionalconsideration here is the minimum thickness D that can be obtained inthe bladder with uniform vertical distribution. This is a function ofthe volume of fluid contained in the bladder, and the overall dimensionsof the bladder, V and H which are shown in FIGS. 1A-1F. In the preferredembodiment shown in FIGS. 1A and 1B, V and H are approximately 25 cm;when filled with 1.4 l of fluid, the thickness D is about 4 cm. This isin marked contrast to other systems on the market, which have a muchgreater thickness D. For example, the CamelBak FlashFlo™, when filledwith 1.4 l of fluid, has a measured thickness D of about 8 cm; othersystems have comparable dimensions. The result of this large thickness Dis an increased moment of inertia, resulting in greater bladder motionand resultant forces on the tissues of the user. Optimal motion controlis thus provided not only by the motion control features of the pack,but also by the dimensions of the bladder. The desired shape of thefilled bladder is one in which the thickness D is minimized, within theconstraints of the vertical and horizontal dimensions V and H.Constraints on the upper limits V and H are determined both by the bodysize of the typical user, and by the increased surface area, andincreased rate of warming of the fluid that results from increasedbladder surface area. It would be possible to reduce D even further, butat the expense of increased surface area of the bladder and pack.Testing has shown that the dimensions specified here provide an optimumbalance of reduced thickness D with minimal surface area, resulting inoptimum motion control without an excessive surface area that wouldcontribute to warming of the fluid contained within the bladder. Testingof prototypes has revealed that a thickness D significantly greater than4 cm results in a large moment of inertia and produces excessivebouncing of the bladder and pack. Therefore, it is desirable, ifdifferent maximum volumes are required, to vary the dimensions V and Hto increase or decrease the maximum volume while still maintaining athickness D of less than about 4 cm.

FIGS. 7A and 7B show the effect of the webbing attachment angle andzipper placement on fluid distribution and pack placement on the user80. In FIG. 7A, the zipper is placed either at the very bottom or at thevery top, or it is oriented vertically. Here it can be seen that thefluid tends to pool at the bottom of the pack 20. Furthermore, the packtends to fall away from the user's back at the top as a result ofunequal distribution of tension from the webbing 42 on the right sideand the webbing 46 on the left side (hidden in this view). FIG. 7B showsthe results of zipper placement and webbing angle described in thepresent invention. Placement of the zipper 25 at the lower portion ofthe pack 20 results in displacement of a portion of the fluid within thepack in an upwards direction resulting in a more equal verticaldistribution of fluid within the pack. The zipper thus acts not only asa compressive member to force fluid upwards, but also as a partialbaffle. By partially isolating the bottom pool of fluid from the toppool of fluid, the bladder behaves not as one large pool, but as twosemi-autonomous smaller pools. As a result, the two partially separatedpools produce far less net motion than one large pool of fluid.Furthermore, placement of both the right and left webbing straps 42 and46 at a positive angle relative to the horizontal axis of the packresults in greater tension across the top of the pack, preventing theupper portion of the pack from flopping away from the user's body.

FIGS. 8A, 8B, and 8C show the effect of webbing angle on distribution oftension across the pack surface. In FIG. 8A, the straps 42 and 46 areoriented parallel to the horizontal axis of the pack. When the pack ismounted about the user's waist, tension is developed in the straps 42and 46 in opposing directions and parallel to the long axis of the packshown in FIG. 2. Here the greatest tension is directly across the packin a horizontal direction. As a result, relative to the middle portionof the pack, tension across the bottom and top is significantly less. Asa result of gravity, fluid tends to pool in the bottom of the pack, andthe top portion of the pack flops away from the user's back, as shown inFIG. 7A. FIG. 8B shows the present design prior to tensioning of thestraps. Because the straps 42 and 46 are placed at an angle relative tothe horizontal axis of the pack, the distribution of tension across thepack is more efficient than that seen in FIG. 8A. Furthermore, placementof the inelastic zipper 25, which prevents stretching of the fabric inthis region, also alters the distribution of forces across the pack. Asa result of both the webbing angle attachment and zipper placement, upontensioning of the waist straps 42 and 46, there is a more evendistribution of tension across the pack as seen in FIG. 8C.

Description and Operation of Alternative Embodiments

Although the above description contains many specifics, these should notbe construed as limiting the scope of the invention, but as merelyproviding illustrations of some of the preferred embodiments of thisinvention. For example, although the zipper placement is chosen for itsmotion-damping qualities, it would be possible, although morecomplicated, to place the zipper elsewhere on the pack, and sew anadditional inelastic ribbon, cord, or adjustable strap in the lowerportion of the pack. Similarly, placement of the straps at an angleabove horizontal produces an increase in tension across the top of thepack, preventing it from flopping away from the user's body. In additionto the adjustable straps shown in FIG. 3, this effect could also beachieved simply by sewing inelastic ribbon or cord into the top lateralportions of the pack; like the zipper, these would increase tension bydecreasing fabric stretch in this region. Many possible variations inthe shape of the bladder are also possible within the constraintsdescribed.

Conclusion, Ramifications, and Scope of Invention

Accordingly, the reader will see that the hydration system for runnersdescribed herein represents a significant improvement over previousdesigns, and solves a long-felt need for runners, particularly those whoreside in hot climates. The flexible bladder can be filled with severalliters of cold liquid and ice to ensure that the fluid will remain coldduring long hot runs. The flexible, elastic, and thermally-insulatingfabric pack attaches securely about the waist, provides superior motioncontrol without restricting movement of the runner's musculature orother soft tissue, and is unobtrusive due to its low profile. The packis pre-stressed and self-adjusting to provide tension as the bladdervolume changes.

1. A hydration system for runners comprising: a) a waist pack formed byjoining at least two sheets of elastic fabric about the perimeter, saidsheets forming an outer layer and an inner layer of fabric, said layersdefining an internal compartment; b) a flexible bladder for containmentof fluid, said bladder having a fluid holding capacity of between about1 and 3 liters, and contained within the inner compartment of said waistpack; c) said waist pack having an inelastic member attached to thefront sheet, said inelastic member being placed in a horizontalorientation within the lower front portion of the pack, said lowerportion being defined as being between 0.15 and 0.5 times the greatestvertical extent of said pack from the lowest vertical extent of saidpack, resulting in motion control as a result of the inelastic nature ofsaid member constricting said flexible bladder within the region of theinelastic member, resulting in a partial baffle effect and more evendistribution of fluid in the vertical direction; d) means for attachingsaid pack about the waist of the user, said means comprising strapsattaching at their proximal ends to left and right side of said pack andbeing secured at their distal ends by buckles about the user's waist; 2.The hydration system of claim 1 where said sheets of elastic fabric arethermally insulating;
 3. The hydration system of claim 1 where saidinelastic member is a zipper;
 4. The hydration system of claim 1 wheresaid waist straps are attached to the lateral edges of the pack, saidstraps being oriented at an angle between 15° and 60° above thehorizontal axis of said pack;
 5. The hydration system of claim 1 wheresaid bladder, when filled to capacity, has a maximum thickness, measurednormal to the surface of the bladder to the surface of the user's back,of about 4 cm or less;
 6. The hydration system of claim 1 and furtherincluding means for increasing tension about the upper portion of thepack, said means including inelastic elements sewn about the upperlateral portions of the pack, thereby reducing stretch and increasingtension in this area;
 7. A hydration system comprising a waist packformed by joining apposed front and back layers of elasticthermally-insulating fabric, said fabric layers being joined about theperimeter and thus defining an inner compartment for containment of aflexible bladder for containing between about 1 and 3 liters; saidbladder having a shape approximating that of an ovoid; means forattaching pack about the waist of the user, said means comprising strapsor webbing attached to the lateral edges of said pack, said straps beingoriented at an angle of between 15° and 60° above the horizontal axis ofsaid pack, said orientation providing increased tension across the upperportion of said pack, said increased tension acting to draw upperportion of said pack and bladder firmly against the body of the user; aninelastic member sewn in a horizontal orientation across the lower frontportion of said pack, said lower portion being defined as being between0.15 and 0.5 times the greatest vertical extent of said pack from thelowest vertical extent of said pack.
 8. The hydration system of claim 7where said inelastic member is a zipper.
 9. The hydration system ofclaim 7 where said bladder, when filled to capacity, has a maximumthickness, measured normal to the surface of the bladder to the surfaceof the user's back, of about 4 cm or less;